Infrared objective lens



Milli HUUI" Oct. 16, 1951 P. H. TAYLOR INFRARED OBJECTIVE LENS FiledJuly 3, 1950 Mil/5.

m5 P4re/vr Irma/var Patented Oct. 16, 1951 INFRARED OBJECTIVE LENSPhilip H. Taylor, Los Angeles, Calif., assignor to Northrop Aircraft,Inc., Hawthorne, Calii'., a corporation of California Application July3, 1950, Serial No. 171,788

2 Claims.

This invention relates to a new and improved infrared objective. Thelens system is a cemented triplet chromatlcally corrected for the Thelens aberrations and also the optical tolerances are now given.

I th 0 i 1 1 0 icron iii $10 "333; $3253 wave eng s m cron an m 7 I Itis an ofijecto'f'tliwsenfinvention to pro- 2,F, ;i;$3?; (empmca menu)vide an infrared lens system essentially free from (5) Zonal 1 :1:-00044 (emp c l tolerance) spherical aberration. astigmatism, distortion,8333,: (extremelyshmp definition) and fulfilling the sine conditionwithout the use (8) jr =+.01514 o an air space- (is; q ifig tfi 1%? 1. isharp deflnmm) Briefly, the invention includes an optical 0b- (11)TADF'I I jective comprising three coaxial cemented com- 'f tan $138832?(extremely sharp definition) ponents which, from front to rear, are anegative 1. mu U... =i-8ggg e y sharp definition) meniscus concave tothe rear. 9. positive meniscus Q :+j0000062 (entirely invlsible) withconvex surfaces, and a negative meniscus Where concave to the front, theobjective being chrois the spherical aberration equal to the M thewavelengths back focal length of the paraxial ray minus the The singlefigure is a diagram illustrating in $23? 3:?ggg zfig g gfig ig zik axialsection a preferred lens assembly accordis the offense against the sinecondition. mg to the present invention The system com- L'Zi 0-LZ e isthe difference in distance of the prises two negative lenses I and andone posi' intersections of the zonal rays on the optical axis tive lens2 assembled and cemented into a single of the wavelengths 1.0 and .6microns, unit. The lens illustrated has an aperture of z 1 i d 0 de 0emcient whi h is f/l0, is 4.0 inches in diameter, and has a 40 inch i g7E 1 r r c effective focal length. In the figure, the radii 25 m ca Y erac0 of the three lenses have been indicated as r1, r2, Coma" coma errorthe tangential planers and r4. Lenses l and 2 are cemented along r2,Coma s is the coma error in the sagittal plane; and lenses 2 and 3 arecemented alone n. ET is the distance from .selecPed focal planeConstruction t for a 4 inch cemented to the focal point of an off axisob ect in the tantriplet of 40 inches focal length, chromatically 30861117181 p (A prime ys refers to the corrected for the infrared regionin accordance image p c with this invention, is as follows: Tan U'M isone-half the 1" number;

Prescription 55 J micron J micron LU minrnn .0 micron, 1.0 micron d.4000 DF-3 1.02005 1. 00930 1.60408 38.16

(12 .0000 BSC-2 1. 5102s 1. 51070 1. 50745 58.17

.4000 DF-3 n=l33.7435

Where Tang. LA is lateral spherical aberration;

TADF' is the true astigmatic diiference of focus;

X t is the distance from a selected focal plane to the focal point of anoff axis object for the principal ray in the tangential plane;

X I is the distance from a selected focal plane to the focal point of anoil? axis object for the 7 principal ray in the sagittal plane;

Prescription 55 NJ micron NJ micron Ni. lion: .0 Ila-cl, 1.0 lien- 71-17. 8158 11- 9. DF-Z l. 6%)05 1. 60936 1. 604m 38. 16 I (11- 6W0 BBC? 1.51623 1. 51070 1. 50745 58. 17 n- 27.9330 di- 4000 DF-3 133. 7435 Distis the measure of distortion. Where The prescription given above caneasily be varied to suit various purposes as may be desired, by a simplescaling procedure.

When the radii, thicknesses and diameters of the component lenses, forexample, are each multiplied by a constant, and when the effective focallength, the back focal length. the linear size of the field, and theaberrations of the original system are multiplied by the same constant,precise values for the new system will be obtained. It is to becarefully noted that speed (or f/no.) and angular size of the field arenot changed. Neither are the optical tolerances changed. It thereforefollows that if a system of given focal length performs satisfactorily,its optical behavior can always be improved by constructing a smallerscale model. Should a larger scale model be desired, consideration mustbe given to the ratio each aberration bears to its tolerance in theoriginal prescription, since this ratio is subject to multiplication bythe scaling constant.

Having thus described and illustrated this invention, it is claimed:

1. An infrared objective comprising three coaxially cemented componentswhich numbering from front to rear is first a negative meniscus concaveto the rear, the second is positive with convex surfaces, and the thirdis a negative meniscus concave to the front, said objective having thefollowing prescription:

r is the radius length for an element surface;

d is the axial thickness of an element;

Nani is the index of refraction for a wavelength of light equal tomicron;

N mum, is the index of refraction for a wavelength of light equal tomlcrcn;

N. 1 is the index of refraction for a wavelength of light equal to 1.0micron;

DF-3 is a dense flint glass; BSC-Z is a borosilieate glass.

2. An objective scaled from the prescription of claim 1 by multiplyingthe radii, thicknesses and diameters of the component lenses, theeffective focal length, and the linear size of the field of saidobjective each by a constant K differing from zero.

PHILIP H. TAYLOR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

